Wireless energy transfer is typically used to operate an electronic device or to charge a battery. For example, a rechargeable battery in an electronic device can be recharged through inductive charging by coupling a transmitter coil in a charging device with a receiver coil in the electronic device. When a signal is applied to the transmitter coil, an electromagnetic field is created and transfers energy to the receiver coil. The receiver coil converts the energy into a signal that is used to charge the battery. But resistive heat and other signal losses are generated as well when the signals pass through transmitter and receiver coils. These resistive heat and signal losses can vary depending on the operating conditions of the coupled coil system, and in some instances can reduce the efficiency of the energy transfer between the charging station and the electronic device.